1. Field of the Invention
The present invention relates to a device that will indicate the tilt of the forks of a forklift. Individual lights may be used to indicate forward, level or back position to give the operator of the forklift a clearer indication of the position of the forks.
2. Prior Art Statement
Industrial forklift trucks are generally comprised of a wheeled chassis having an operator compartment, a forward mounted, upwardly directed mast and a means for moving the truck. The operator compartment contains operating controls and a seat for an operator. The forward mounted, upwardly directed mast is tiltable relative to the wheeled chassis by an hydraulic cylinder and carries a pair of forward directed forks which are mounted for vertical sliding movement along the mast. The forks are adapted to be inserted within a pallet base that supports a load to be carried and positioned by the forklift. Preferably, the forks are maintained in a generally horizontal level orientation to prevent damage to the product, the pallet, the forklift or to prevent injury to workmen. It is also important to essentially maintain the forks in a generally horizontal level orientation while positioning a pallet on a stack of pallets in order to ensure proper fit on the top of the stack and eliminate the possibility of capsizing the stack of pallets.
Wooden pallets are often used as supports and to separate stacked items by a space into which the fork of the forklift is inserted in order to move the pallet and the load thereupon. The insertion between the pallets is usually effected by driving the forklift forward so that the forks slide between the pallets. The fork is then lifted to raise the upper pallet and the objects thereon. When articles are stacked upon one another using wooden pallets, inserting the forks between layers requires that the fork be properly positioned both with respect to height and tilt angle of the fork. The tilt angle of the fork is important for correct and trouble free sliding under the pallet. With wooden pallets, the fork is inserted into an opening in the pallet between two layers of stacked objects. When the angle is incorrect, the rigidity of the pallet can cause the fork to get stuck or the fork may pierce the goods placed upon a pallet or may push a pallet off a stack. These problems may occur whether the angle of the fork is tilted too far forward or too far backward so getting the tilt angle correct for fork insertion between pallets is critical and requires substantial practice. Height of the fork from a base surface is relatively easy as the tip of the fork may be readily observed by the operator but the angle of the fork is far more difficult because the operator is not well positioned for visually determining the tilt angle.
When the forklift truck is transporting a load on an inclined surface, it may be further necessary to adjust the angular position of the mast to bring the forks to a more horizontal position. Additionally, in operations where the forks are at a very high elevation, it may be necessary to adjust the angle of the mast to maintain the center of gravity of the loaded truck within safe operating limits.
In view of these concerns, level indicating devices operating on a plumb bob principle that indicate the position of the forks relative to a true vertical have been developed for forklifts. For instance, see U.S. Pat. No. 3,312,361 issued on 4 Apr. 1967 to Foster; U.S. Pat. No. 3,865,265 issued on 11 Feb. 1975 to Brudi, et al., and U.S. Pat. No. 3,883,021 issued on 13 May 1975 to Wilhelm. These devices often produced inaccurate indications due to foreign matter, physical damage and/or lateral movement of the forklift relative to the vertical plane. Therefore, there is a great need for a forklift fork indicating device that indicates the position of the forks relative to the wheel base.
Improvements have been made to pendulum type indicator by protecting the swinging pendulum which pivots on a post attached to the mast. The pendulum also has an indicating arm attached to its upper end at the pivot which extends toward the rear of the mast so it is observed by the operator. A sliding pointer near the rear face of the mast has a pin protruding through a slot in the indicating arm so that when the mast moves the sliding pointer moves in concert with the direction of movement of the mast. For instance, see the U.S. Pat. No. 6,941,666 B2 issued on 13 Sep. 2005 to William J. Parish. Maintenance has been found to be significant with the pendulum and inaccuracies have been observed as with older pendulum types.
A further improvement in pendulum devices is found in U.S. Pat. No. 6,981,331 B1 issued on 3 Jan. 2006 to Poe, Jr., et al. Poe, Jr., et al., provide a magnetically dampened device that is affixed to the upright column of the fork assembly, however, it has been found that inaccuracies still occur during transit and lateral movements. Furthermore, as with all pendulum indicators, the indicator actually indicates the position of the forks relative to a true vertical which leads to inaccuracies on inclined surfaces. Therefore, there is a great need for a fork position indicator that indicates a fork attitude relative to the surface upon which the fork lift is placed.
It has been known to provide an extension to the cylinder which receives a movable connector in the free end thereof wherein the movable connector is rotatably attached to a variable potentiometer fixed to the fork assembly frame. The angle of the fork relative to the frame is displayed to an operator on an indicator preferably mounted in a position where the operator can view both the height of the fork and the angle indicator. For instance, see the U.S. Pat. No. 5,131,801 issued on 21 Jul. 1992 to Clayton C. Melanson. It has been found that the variable potentiometer and the movable connector are subject to damage as the components insufficiently robust and exposed to the forklift environment. Therefore, there is still a need for an indicating device for a forklift that is robust and generally protected from damage.
Another prior art device provides a finger on the upright bar which touches one of the limit switches when the mast reaches either a maximum forward or rearward angle. It is assumed that the upright bar and finger are associated with the cylinder and the limit switches are affixed to the fork frame. The two electric eyes are assumed to determine maximum right and left side shifting of the forks. For instance, see U.S. Design Pat. No. D 351,111 issued on 4 Oct. 1994 to John W. Sheakley. The device only indicates the maximum forward and rearward positions and cannot indicated a level condition. Therefore, there is still a need for a fork position indicator that indicates a fork attitude relative to the surface upon which the fork lift is placed including indicating a null position where the mast is perpendicular to the forklift surface.
It is further known to provide a forklift indicating device which contains an electronic bubble level sensors such as an opto-electronic leveling device that accurately determines the position of the bubble. For instance, see U.S. Publication 2009/0114485 A1 published on 7 May 2009 to Richard T. Eggert. Such a device is extremely expensive to manufacture and therefore not within the reach of many forklift owners. Thus, a need now exists for a simple, robust and accurate fork position indicator that indicates a fork attitude relative to the surface upon which the fork lift is placed including indicating a null position.
Also known is a device provided with a plurality of Hall effect transistors arranged linearly along a box affixed to the tilt cylinder. A rod or tape passes alongside the Hall effect transistors and carries a magnet which causes a Hall effect transistor to change state when the magnet passes nearby. The transistors are arranged to indicate a tilt angle of the mast. For instance, see the U.S. Pat. No. 5,749,696 issued on 12 May 1998 to Marc Johnson. Though apparently accurate, providing a plurality of Hall effect sensors is also extremely expensive and not widely used. A need still exists for a simple, robust and accurate fork position indicator that indicates a fork attitude relative to the surface upon which the fork lift is placed including indicating a null position.
Finally, it is known to provide an electronic sender/receiver which sends out a signal that is reflected by a reflector mounted on the operator side of the mast. The degree of inclination is determined by the distance of the reflector from the sender/receiver. For instance, see the U.S. Publication 2008/0202856 A1 published on 28 Aug. 2008 to Fossier, et al. Movement of the reflector corrupts the signal reflection resulting in inaccuracies. The cost of the electronics may also be significant. Accordingly, a simple, robust and accurate fork position indicator which comprises a simple operator indicator, at least one switch, an indicator rod and a mounting lug wherein the indicator rod is greatly needed.